Look up the term. Return to the working surface.

An environment variable listing the directories your shell searches for executables. When you type `node`, the shell scans $PATH left-to-right; the first match wins. Why version managers (nvm, pyenv) work the way they do.

The discipline of making apps usable by everyone — keyboard navigation, screen readers, color contrast meeting WCAG-AA. Lighthouse audits this automatically.

Four properties that guarantee data integrity in a relational database: Atomic, Consistent, Isolated, Durable. The reason relational DBs dominated for 50 years.

Architecture Decision Record — a short numbered file (`docs/adr/0001-use-sqlite.md`) capturing one significant design decision with context, options considered, and rationale. Institutional memory that survives team turnover.

An AI system that can plan multi-step tasks (write code, search the web, modify files) — not just answer one question. Antigravity's built-in assistant and Claude/Cursor/Copilot are examples.

Google's free browser-based AI coding platform. Used in Lesson 01 as a beginner-friendly first contact with AI-assisted development before moving to VS Code in Lesson 02.

Application Programming Interface — a contract for how programs ask another program for data. Specifies endpoints (URLs), HTTP methods, headers, body shape, and response shape.

The secret string that authenticates your server to an LLM provider (OpenAI, Anthropic, Google). Lives in `.env`, listed in `.gitignore`, never shipped to the browser.

Code that runs on a server you control. Users can only call it via HTTP. Where business logic, authentication, database access, and secret-bearing third-party API calls belong.

An LLM call wrapped at both ends by your code: your prompt template controls the input, your validation controls the output, the model is the engine in between. The discipline that turns AI demos into AI products.

A named pointer to a commit. Creating a branch is O(1) — instant, free, no copying — because nothing actually moves; only the pointer is named. The professional Git workflow uses one branch per feature.

Prompting technique where you ask the model to "think step by step" before producing the final answer. Materially improves quality on reasoning, math, and multi-step tasks.

An outbound-only secure tunnel from your machine to Cloudflare's edge network. Provides a public HTTPS URL without opening any inbound port on your router. Free for personal use.

A snapshot of your project's files at a moment in time, identified by a SHA-1 hash. Git history is a graph of commits; each commit points to its parent (or parents, for merge commits).

A way to package an application plus its environment into a single shippable unit. Containers share the host kernel and use Linux namespaces, cgroups, and union filesystems for isolation. Not a VM.

Cross-Origin Resource Sharing — a browser security mechanism that blocks frontend-on-domain-A from calling backend-on-domain-B by default. The `cors` middleware on your server is how you opt-in to allowing specific origins.

Software designed to store data persistently and retrieve it efficiently. Two big families: relational (SQL — SQLite, Postgres) and document/key-value (Mongo, Redis, DynamoDB).

The dominant container runtime and its surrounding tooling. A user-friendly UX wrapper around Linux kernel features (namespaces, cgroups, union filesystems) that already existed for years.

A tool for defining and running multi-container applications via a single docker-compose.yml file. Resolves "but I have a different version of Postgres" by codifying the entire stack as version-controlled YAML.

A text file with the recipe for building an image. Each instruction (FROM, COPY, RUN, CMD) creates a new layer; layers are cached and reused across builds.

What the UI shows when a list, feed, or section has no data yet. The first impression for every brand-new user — treat it with the same care as the populated state.

A specific URL on an API where a resource or operation is exposed. `/api/scores`, `/users/42`, `/weather` are all endpoints.

The most popular Node.js framework for building HTTP servers. Mental model: routes (URL + verb) → handler functions (`req` in, `res` out) → JSON response. Composable via middleware.

A plugin that adds capability to VS Code: linting (ESLint), formatting (Prettier), Git history (GitLens), AI assistance, language support. Extensions are the engine of VS Code's productivity.

A pre-written default the user sees when the model API fails (timeout, 4xx, 5xx, network down). Non-negotiable in production: a failed AI call must never leave the user with a broken UI.

Including 2-3 example input/output pairs in the prompt to anchor the output shape. Dramatically improves consistency for structured tasks. Beats zero-shot for almost everything.

Code that runs in the user's browser or app. HTML, CSS, JavaScript. Anything in the frontend is visible to every user — never put API keys or business rules here.

A distributed version control system created by Linus Torvalds in 2005. Stores code history as a directed acyclic graph of snapshot commits. Runs locally on your machine; works offline.

A cloud-based hosting service for Git repositories, owned by Microsoft. Adds web UI, pull requests, code review, GitHub Actions for CI/CD, and the social features that made it the default home for open source.

The action verb in an HTTP request. GET reads, POST creates, PUT replaces, PATCH updates, DELETE removes. Same path, different verb = different operation.

Integrated Development Environment — software where you write, run, and debug code. VS Code is the most common IDE in 2026; alternatives include JetBrains, Sublime Text, vim/emacs.

A property: doing the same operation multiple times produces the same end state. GET / PUT / DELETE are idempotent by spec; POST is not. Production APIs use idempotency keys to make POST retry-safe.

A template — a packaged filesystem snapshot, in layers, that contains your app and its dependencies. A container is a running instance of an image. One image, many containers.

A data structure the database maintains so queries on specific columns stay fast as the table grows. `CREATE INDEX idx_score ON scores(score DESC)` makes "top 10 scores" stay constant-time even with a million rows.

JavaScript Object Notation — a text data format with exactly six types (object, array, string, number, boolean, null). The de facto wire format between systems on the modern web.

A provider feature that forces the model to return valid JSON, often against a schema you specify. The contract that lets your code reliably parse model responses without fragile string handling.

A separate document declaring what shape valid JSON must have — required fields, types, value patterns. Used to validate incoming API requests and to generate client SDKs.

Chrome DevTools' built-in audit for Performance, Accessibility, Best Practices, and SEO. Run it in 30 seconds; the first audit always finds at least one easy improvement.

Large Language Model — the actual AI behind ChatGPT, Claude, Gemini, etc. A trillion-parameter neural network running on a cluster of GPUs. Accessed via HTTP APIs from your code.

A 3D object in Three.js: geometry (the shape, defined by vertices and triangles) plus material (the surface look — color, shininess, lighting response). Same geometry + different material = same shape, different feel.

Small functions in Express's request-processing pipeline. Each one either passes control to the next (`next()`) or short-circuits with a response. Authentication, validation, logging, and error handling are all middleware.

The Unix operator that sends one command's output as input to another. `ps aux | grep node` filters running processes to just Node ones. The composition primitive that makes the terminal a Lego set.

An SQL statement with `?` placeholders for runtime values. The database substitutes values safely (escaped, not concatenated) — preventing SQL injection. Always use prepared statements when SQL meets user input.

An attack where user-supplied text contains instructions that override your system prompt ("ignore previous instructions and..."). The defense: delimit user input clearly, instruct the model to treat it as data, validate output.

A formal proposal on GitHub to merge one branch into another, with code review and discussion. The professional workflow: branch → commits → push → open PR → review → merge.

The front-door file every GitHub project needs. Recruiters spend ~30 seconds on a portfolio repo; the README is the entire conversation. Six sections: title, demo, features, quick start, architecture, license.

A project under Git's tracking — a folder plus its complete history of changes. On GitHub, it's also a URL where the project lives publicly or privately.

A way of designing HTTP APIs around resources (URLs) and HTTP verbs (GET, POST, PUT, PATCH, DELETE). The same path with different verbs does different things. The dominant API style on the web.

A server that takes public requests and forwards them to a private origin. Cloudflare Tunnel, Nginx, AWS API Gateway are all reverse proxies. Provides TLS termination, caching, and protection.

Serialize: turn an in-memory object into a JSON string (`JSON.stringify`). Deserialize: turn a JSON string back into an object (`JSON.parse`). Every API call uses both directions.

VS Code's configuration file. Anything in the GUI Settings UI also lives as a key here. Version-control it, share with teammates, sync across machines via Settings Sync.

The program inside the terminal that interprets your commands. The two most common: bash (older, default on most Linux) and zsh (default on modern macOS, with richer features).

Structured Query Language — the query language relational databases speak since 1974. Five statements (CREATE TABLE, INSERT, SELECT, UPDATE, DELETE) cover ~95% of daily database work.

A library, not a server — a relational database that lives in a single file. The most-deployed database engine in the world (every Android phone, every iPhone, Firefox, Chrome, etc.). Perfect for personal projects.

A 3-digit number in every HTTP response. Five families: 2xx success, 3xx redirection, 4xx client error (your fault), 5xx server error (their fault). Tells you which side's bug to debug.

A first message to an LLM that sets persona, constraints, and tone for the conversation. Production code; version-controlled. Small wording changes produce dramatically different outputs.

A text-only interface to your computer. You type a command; a shell (bash, zsh) interprets it; a tool runs; output is printed. The portable working surface every senior engineer uses daily.

A JavaScript library that makes 3D rendering in the browser approachable. Wraps WebGL, exposes scenes / cameras / meshes / materials. Used by Google Earth, parts of Fortnite's frontend, and many WebGL-based products.

The unit LLM APIs charge in. Roughly 3-4 characters of English text per token. Pricing is quoted per million tokens; input and output are priced separately. Cheap models are 10-100× cheaper than frontier models.

A senior-engineering discipline: at the end of every milestone, stop and verify the system actually works end-to-end on a network you don't fully control. Catches regressions and assumption-drift before users do.

Microsoft's free desktop code editor — the de facto standard for professional engineering work. Built on Electron, extensible via marketplace, configurable via settings.json. Most developers spend most of their working hours inside it.

The browser API that lets JavaScript send instructions to your GPU. Three.js calls WebGL under the hood. Why 3D in the browser is fast: the parallel-math hardware is doing the heavy lifting.